The most common method. The central server sends the entire file to everyone who needs it - this is how the HTTP and FTP protocols work. The only advantage of this method is that it is easy to implement and use. This model can fail - once the server becomes too popular, and as soon as the data size begins to be too large.
Mirrors
The concept of "mirroring" only partially solves this problem, because it requires a complex configuration of "mirroring" the servers and the distribution of the load between them.
Client-client (p2p)
The second most popular are p2p systems, such as Kazaa, eDonkey, Gnutella, Direct Connect, etc. Network users exchange files directly by connecting to each other.
Advantage:
The files do not need to be on the same server.
Disadvantages:
It's impossible to track the contents of files. That's why these networks have gained immense popularity among music lovers, films and especially warez.
the problem was popular data, which is drawn by the largest number of people, because the new files literally "lined up," the download speed decreased in proportion to the number of requests for this file.
In most p2p systems, the number of connections between users is limited, and often users who apply for a file simply receive a denial.
Fully downloaded files were also a problem for users, since it is not possible to determine in advance whether the whole file is "whole" or not.
Result of these problems was the fall in the popularity of many networks and the introduction of prohibitive rules for users participating in them.
Client-client method (torrent)
However, using the experience of Usenet, where information is distributed between users on the chain, where each user can download information and at the same time make his own without destroying the logical integrity of the group. As a result, files distributed by Usenet have become the most convenient way for mass distribution of files. As a consequence, newsgroups have evolved into streams of messages from digital data.
Bittorrent is similar to Usenet in this. It is most suitable for the distribution of new products, which are of interest to a large number of people. Old or little used files are distributed slowly or not at all.
All who download this file are simultaneously and distributors of the fragments they have already downloaded. So you download the missing fragments of the file at the same time distribute the fragments you have already downloaded to others. Thus, you "help" others and "others" in turn "help" you.
Result is such that the download speed is ideally limited only by the bandwidth of your channel. In real life - it depends heavily on the number of people downloading this file. That is, the more people, the more the number of potential sources of distribution of this file. And since the torrent client supports multithreading, then as a result - higher speed!
